Protecting quantum spin coherence of nanodiamonds in living cells

Because of its superior coherent and optical properties at room temperature, the nitrogen-vacancy (N-V) center in diamond has become a promising quantum probe for nanoscale quantum sensing. However, the application of N-V-containing nanodiamonds to quantum sensing suffers from their relatively short spin coherence times. Here we demonstrate energy-efficient protection of N-V spin coherence in nanodiamonds using concatenated continuous dynamical decoupling, which exhibits excellent performance with a less-stringent microwave-power requirement. When this is applied to nanodiamonds in living cells, we are able to extend the spin coherence time by an order of magnitude to the T-1 limit of 30 mu s. Further analysis demonstrates concomitant improvements of sensing performance, which shows that our results provide an important step toward in vivo quantum sensing using N-V centers in nanodiamond.